A Review of Relevant Factors in Substance Selection for Direct Posterior Restoratives
Abstract
The type of material chosen for posterior restorations, commonly known as tooth fillings, in this case for molars specifically, depends on many variables. The durability, strength, and ease of application of the material are important, but at the same time so are the needs of the patient, so factors like esthetics need to be considered as well. Posterior restoratives require a particularly durable material, because the molars receive the majority of stress during mastication. Fillings are a preventative measure, "a seal" that protects the tooth from further decay. If this can be prevented successfully with a compatible filling material for a significant period of time, the patient can help postpone the most likely inevitable extraction of the tooth. Unfortunately, a perfect restorative material has not yet been invented, and thus, bacteria consistently find a way to break the barrier of every restoration. However, many new technological advances have occurred within the last two decades that will aid in the eventual discovery of the ideal material for restoratives.
Introduction
There are two main types of fillings: amalgam and resin. Amalgam is an alloy usually composed of about 50% mercury and the remainder consists of silver and trace amounts of copper, tin or zinc. This alloy of metals has been used in dentistry for nearly 200 years to reconstruct decayed teeth, particularly those located posteriorly. Its popularity and success arises from its cheap cost, durability and ease of use. However, the use of mercury in dentistry has become more controversial recently because analytical chemistry techniques have shown that there is a continuous release of low levels mercury vapor from dental amalgams. The level and release is dependent on the size of the filling, tooth and surface placement, food texture, chewing, tooth grinding, tooth brushing, and surface area, composition and age of the amalgam [Bates 2006]. The other filling genre is called resin, which is composed of many different varieties of polymers that vary in chemical composition. This type is more often used on the frontal teeth because it is more esthetically pleasing and does not require such durability as the posterior molars.
The various types of resin esthetic restorations and their positive and negative qualities further complicate the ongoing debate between amalgam and resin. Examples of resin include, glass ionomers, compomers, composite resin. The main difference in composition between these resins is the chemical attributes. Unlike amalgam fillings, the resin material contains desirable attributes such as fluoride release, wear resistance, low polymerization shrinkage, and low polymerization stress [Burgess 2011]. Fluoride strengthens the structure of the tooth, the low shrinkage sometimes occurs after filling is completed, where the material shrinks allowing bacteria to enter the cavity again, and the more a material is resistant to stress, the less likely the polymerization shrinkage will occur. Therefore, the use of amalgam and resin fillings can be determined based on the type of procedure involved.
Amalgam restorations
Posterior amalgam restorations have declined in popularity recently, but their usage must not be completely ignored. Amalgam fillings have a history of clinical success. To start with, an amalgam has good moisture tolerance since it does not bond to tooth structure chemically [Burgess 2011]. Therefore, the restoration procedure is much simpler, because it is not necessary to keep the tooth isolated and in dry conditions like in resin restorations. Since amalgam is a metal alloy it has the typical properties of metals, an amalgam filling is malleable and can be easily formed into shape of tooth, but at the same time it is also strong and durable. Limitations include galvanism [Burgess 2011], where a battery effect occurs in the mouth. It is caused by the amalgam’s composition of two metals, usually silver and mercury, in liquid medium, saliva. This scenario produces an electric current, which then leads to the break down of the amalgam filling. Other limitations caused by the amalgam’s metal properties are high thermal conductivity and the absence of adhesion to dental tissue [Burgess 2011], which often requires the additional removal of healthy tooth structure. The last main deterrent is its poor esthetics, and amalgam fillings are used typically on posterior restorations.
In one of the first population-based studies conducted [Correa 2012], individuals with different types of restorative materials were interviewed and their responses were quantified. It was possible to divide individuals with composite fillings vs. those with resin restoratives based on factors such as their education level, socio-economic status, gender, cultural background, and age [Correa 2012]. Molar teeth are associated more frequently with amalgam fillings, which is a logical conclusion. However, since dentists rely on adhesives more often currently in combination with the resin compound, more people have been accepting it when they have an increased number of tooth surfaces in need of restoration.
The metal properties of alloy of an amalgam, allow it to simply be maneuvered to fit into the cavity for the restoration. There is no chemical bond; the amalgam and the cavity of the tooth fit together like two pieces of a puzzle. In resin fillings, on the other hand, bonding material must be applied before the resin in order to form a chemical bond between the tooth surface and the resin. Amalgam does not require a bonding material, but one has been developed called the bonded amalgam technique using adhesives. The most successful kind is called “4-META-based Amalgambond Plus (Parkell)”. It works by having a bonding agent bond to dentin with a hybrid layer. Dentin is the second layer of the tooth from outside in that comes after the outermost layer, enamel, which forms the crown visible on the outside [see Fig.1] [Burgess et al 2011]. The bonding resin to amalgam attachment is still mostly mechanical, not chemical. In 1992, as part of a study, the average bond strength between the existing amalgam and the new amalgam with Amalgambond (Parkell) was 105.68 kg/cm2 (10.37 MPa)[Chang 2004]. Therefore, the combination of both a mechanical bond of the amalgam filling, as well as the new Parkell bonding agent can allow the restored tooth to better resist fracture.
[fig. 1: [Human tooth. (2012, December 7). In Wikipedia, The Free Encyclopedia. Retrieved 08:45, December 7, 2012, fromhttp://en.wikipedia.org/w/index.php?title=Human_tooth&oldid=526877761]
Resin Restorations
The material selection for both posterior teeth restoration with resin compounds as well as that with amalgam is dependent upon the same factors: the patient’s age, caries (cavity) risk, esthetic requirements, how well the tooth can be isolated, and functional demands of the restoration [Burgess 2011]. In resin types, compomers, glass ionomers, and composite resins have the ability to bond to the tooth structure chemically, reinforce the tooth, fulfill esthetic requirements, behave as good thermal insulators and have fluoride release. On the other hand, a resin reconstruction procedure especially on molars has clinical limitations. It requires more time and attention to detail. Additionally, there are postoperative risks of polymerization shrinkage [Davidson, 1997] possible as a result of difficult procedure where there can be poor adhesive placement, all of which lead to possible leakages at the tooth surface and tooth sensitivity.
There is a category of resin materials that has a stronger ability to release fluoride. This is a very important quality, because fluoride is a natural element included in toothpaste, as well as some water supplies that strengthens the tooth structure. Fluoride application is the most effective way of preventing caries and plaque, especially in the primary, developing teeth of children. Therefore, if the element is present in high amounts in a tooth filling as well, then the filling not only seals the cavity from destroying the tooth further, but it also strengthens the tooth in order to protect it against future caries.
A tooth’s structure made up of enamel, dentin, and pulp, constantly undergoes demineralization and remineralization processes. The 2mm thick outermost enamel layer consists of 96% calcium hydroxyapatite, 3% water and 1% proteins and lipids [Choi 2010]. During dental erosion, the enamel surface undergoes irreversible acidic dissolution. This is where the additional calcium fluoride layer [Gibson, 2011], made possible by the release of fluoride, would protect the regularly bare enamel surface. Bacteria are not involved in the erosion process. Instead, acids present in the food that we consume decalcify the enamel layer and leave the normally smooth tooth with an irregular surface. This effect is called “acid-etching” [Choi 2010].
The exact chemistry behind fluoride’s stellar protection of tooth enamel is still under debate. However, it is known that in already affected teeth, fluoride acts to reduce caries. It can do this by preventing bacteria from metabolizing carbohydrates on the enamel of the tooth [Gibson 2011]. Fluoride may also stimulate remineralization of the tooth, especially when exposed to increased levels of acid. This would in turn protect the tooth and reduce the tooth’s solubility after acid-etching.
It is possible, then, that fluoride can still offer protection to a healthy tooth. That is the theory behind how fluorination may still be useful to healthy permanent teeth in addition to healthy, developing primary teeth. The second step described above demonstrates the protective action of a fluoride-releasing resin material. Specifically, a material that allows the uptake of fluorine from the environment has a high “fluoride recharge,” or it may have the opposite, a high “fluoride release.” With added fluoride from the filling, for example, the tooth can then reduce caries in the other two ways. For the last step, the possible mechanism of action to reduce “the tooth’s solubility during subsequent acid attacks” , such as the erosive process, is the formation of a calcium fluoride layer forms in order.
The types of fluoride-releasing materials for restoration are glass ionomers, high-viscosity glass ionomers, resin-modified glass ionomers, and compomers. Glass ionomers release high levels of fluoride but they have low bond strengths, low wear resistance and medium fluoride recharge. In order to increase their bond strength, a conditioner or primer, usually a weak inorganic acid, is added to the tooth surface prior to the bonding process. This kind of conditioner is called an adhesive as well[Van Meerbeek 1998]. Using this kind of “super-glue” for teeth has become increasingly popular, and as a result, many clinical studies were conducted to test the effectiveness of different types [Tyas 2004]. High-viscosity glass ionomers release high levels of fluoride, have medium bond strength, overall strength, wear and fluoride recharge. The fluoride releasing composites, ironically, release low levels of fluoride and have a low fluoride recharge. They are not appropriate for a high caries risk patients, even though they also have the best wear resistance and toughness out of the fluoride releasing materials. The resin-modified glass ionomers have nanofillers added. This reduces particle size, and thus, creates a smoother, more esthetic appearance. Its release high levels of fluoride also increases long-term survival of the tooth and filling and is therefore, appropriate for a high caries risk patient. Compomers consist of a blend of resin composite and glass ionomers. They are successful to use on children’s teeth [Tran 2003] because the bonding system for compomers uses adhesive. This blocks some of the fluoride uptake in dentin, allowing for most of the fluoride from the compomer to be released on outer tooth surface. The primary and developing teeth of children need more protection on the outer surface as they begin to grow. Additionally, even though the mercury fumes from amalgam have proved to be harmless by many studies, parents still prefer that their children opt for the “safer” and more aesthetically pleasing resin tooth-colored materials [Tran 2003].
Composite resin is another choice of resin that has its own set of setbacks. It was not a very popular choice for posterior restorations because of its poor wear resistance. It was mainly used on bicuspids (premolars) because of its esthetic appeal. Over time, however, clinical trials testing wear resistance gained positive results and the popularity of the resin grew. con: composite resin shrinkage during polymerization [Bausch 1982]. Shrinkage causes eventual breakdown and thermal sensitivity. In order to decrease this effect, it is possible to use an elastic resin base layer of a lowly viscous substance before administering the composite resin, so that the strain will be minimized[Bausch 1982]. Another method used to decrease shrinkage is using LED lights. The procedure of the filling with composite resin involves placing visible light cured composite is placed in prepared cavity and curing it with light in 2mm increments. There are photoinitiators in the resin made of camphoroquinone, usually in the presence of an amine accelerator or catalyst. They are are activated by the visible light and the catalyst. This activated diketone causes the dimethacrylate resin monomers to polymerize. However, if there is a combination of photoinitiator types, there may be a problem because they need to absorb different wavelengths of light in order to react. Usually LED lights are used but quartz-tungsten-halogen or plasma arc curing lights polymerize all photoinitiators. Often the wrong type of light is used, which leads to low wear resistance in the final cured product.
Flowable composites are similar to composite resins, but with a lower viscosity. The flowable composites contain a lower filler load which allows them to better adhere to the cavity surface. There have been many studies conducted about whether this may reduce polymerization stress, but no clear consensus based on numerous has been reached. [Chung 2004]. A drawback of this material is that the lower filler load may reduce wear resistance. However, the percentage of filler may be chosen relative to type of tooth in concern. Flowable composites have higher polymerization shrinkage than composite resins because the flowables are more elastic [Davidson 1997]. It would make sense then, that they provide stress relief . However, since this has not yet been proven, the main use of this composite is for cavity adaptation. Unfortunately, in composite resins the polymerization shrinkage is about 3.7%-0.9%. There was a study conducted on six commercially available composite resins, each that were activated either either where the polymerization shrinkage was measured using a dilatometer and a mercury-filled capillary.
A new low stress material has been invented that reduces the internal stress from polymerization shrinkage. This substance can now be polymerized in 2mm instead of 4mm. The basis behind the SDR technology is the Polymerization modulator, which is embedded chemically in the resin backbone. This modulator interacts with the photoinitiator (usually camphorquinone) to regulate a slow modulus development, while at the same time still allowing a steady rate of polymerization or conversion of the material. Before SDR, the only way to control the modulus was by regulating the overall modulus development. This modulator allows more linear and branching chain propagations and conversions in the polymerization process.
Conclusion
Amalgam usage may have decreased, because the resin composite has grown, branched, and evolved to become a viable and aesthetic replacement; however, each restorative material has its own specific benefits and disadvantages. In the end, the type of material for reconstruction should be personalized to each clinical situation and needs of the patient. The increased number of studies and new developments in esthetic composite resins that cause low polymerization shrinkage, low stress, increased durability etc., present the patient with a variety of more appealing options, as opposed to simply black or white, amalgam or resin. Finally, as a result of the competition to concoct the ideal restorative, the accuracy in their chemical and physical properties of posterior restoratives has increased because of the strong competition for the ideal material.
Works Cited
Bates, M. N. (2006). Mercury amalgam dental fillings: An epidemiologic assessment. International Journal of Hygiene and Environmental Health, 209(4), 309-316. [DOI ]
Bausch, J. R., de Lange, K., Davidson, C. L., Peters, A., & de Gee, A. J. (1982). Clinical significance of polymerization shrinkage of composite resins. The Journal of Prosthetic Dentistry, 48(1), 59-67. [DOI ]
Chang, J. C. (2004). Amalgam repair with a 4-META resin. The Journal of Prosthetic Dentistry, 92(5), 506-507. [DOI ]
Choi, S., Cheong, Y., Lee, G., & Park, H. (2010). Effect of fluoride pretreatment on primary and permanent tooth surfaces by acid-etching. Scanning, 32(6), 375-382. [DOI ]
Chung, S. M., Yap, A. U. J., Koh, W. K., Tsai, K. T., & Lim, C. T. (2004). Measurement of poisson's ratio of dental composite restorative materials. Biomaterials, 25(13), 2455-2460. [DOI ]
Correa, M. B., Peres, M. A., Peres, K. G., Horta, B. L., Barros, A. D., & Demarco, F. F. (2012). Amalgam or composite resin? factors influencing the choice of restorative material. Journal of Dentistry, 40(9), 703-10. [DOI ]
Davidson, C. L., & Feilzer, A. J. (1997). Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives. Journal of Dentistry, 25(6), 435-440. [DOI ]
Lubisich B. Erinne, Thomas J. Hilton, Jack L. Ferracane, Hristina I. Pashova, & Bruce Burton. (2011). Association between caries location and restorative material treatment provided. Journal of Dentistry, 39(4), 302-308. [DOI ]
Gibson, G., Jurasic, M. M., Wehler, C. J., & Jones, J. A. (2011). Supplemental fluoride use for moderate and high caries risk adults: A systematic review. Journal of Public Health Dentistry, 71(3), 171-184. [DOI ]
Giovannetti, A., Goracci, C., Vichi, A., Chieffi, N., Polimeni, A., & Ferrari, M. (2012). Post retentive ability of a new resin composite with low stress behaviour. Journal of Dentistry, 40(4), 322-328. [DOI ]
Ilie, N., & Hickel, R. (2011). Investigations on a methacrylate-based flowable composite based on the SDR™ technology. Dental Materials, 27(4), 348-355. [DOI ]
John O Burgess, & Deniz Cakir. (2011). Material selection for direct posterior restoratives. Dental Economics, 101(9), 34A-34A,35A,36A,37A,38A,39A,40A,41A,42A,43A,44A,45A. [pdf ]
Lambrechts, P., Goovaerts, K., Bharadwaj, D., De Munck, J., Bergmans, L., Peumans, M., & Van Meerbeek, B. (2006). Degradation of tooth structure and restorative materials: A review. Wear, 261(9), 980-986. [DOI ]
SABATINI, C., CAMPILLO, M., & AREF, J. (2012). Color stability of ten resin-based restorative materials. Journal of Esthetic and Restorative Dentistry, 24(3), 185-199. [DOI ]
Tran, L., & Messer, L. B. (2003). Clinicians choices of restorative materials for children. Australian Dental Journal, 48(4), 221-232. [DO I]
Tyas, M., & Burrow, M. (2004). Adhesive restorative materials: A review. Australian Dental Journal, 49(3), 112-121. [DOI ]
Van Meerbeek, B., Perdigão, J., Lambrechts, P., & Vanherle, G. (1998). The clinical performance of adhesives. Journal of Dentistry, 26(1), 1-20. [DOI ]
Wang, W., DiBenedetto, A. T., & Jon.Goldberg, A. (1998). Abrasive wear testing of dental restorative materials. Wear, 219//(2), 213-219. [DOI ]
A Review of Relevant Factors in Substance Selection for Direct Posterior Restoratives
Abstract
The type of material chosen for posterior restorations, commonly known as tooth fillings, in this case for molars specifically, depends on many variables. The durability, strength, and ease of application of the material are important, but at the same time so are the needs of the patient, so factors like esthetics need to be considered as well. Posterior restoratives require a particularly durable material, because the molars receive the majority of stress during mastication. Fillings are a preventative measure, "a seal" that protects the tooth from further decay. If this can be prevented successfully with a compatible filling material for a significant period of time, the patient can help postpone the most likely inevitable extraction of the tooth. Unfortunately, a perfect restorative material has not yet been invented, and thus, bacteria consistently find a way to break the barrier of every restoration. However, many new technological advances have occurred within the last two decades that will aid in the eventual discovery of the ideal material for restoratives.Introduction
There are two main types of fillings: amalgam and resin. Amalgam is an alloy usually composed of about 50% mercury and the remainder consists of silver and trace amounts of copper, tin or zinc. This alloy of metals has been used in dentistry for nearly 200 years to reconstruct decayed teeth, particularly those located posteriorly. Its popularity and success arises from its cheap cost, durability and ease of use. However, the use of mercury in dentistry has become more controversial recently because analytical chemistry techniques have shown that there is a continuous release of low levels mercury vapor from dental amalgams. The level and release is dependent on the size of the filling, tooth and surface placement, food texture, chewing, tooth grinding, tooth brushing, and surface area, composition and age of the amalgam [Bates 2006]. The other filling genre is called resin, which is composed of many different varieties of polymers that vary in chemical composition. This type is more often used on the frontal teeth because it is more esthetically pleasing and does not require such durability as the posterior molars.The various types of resin esthetic restorations and their positive and negative qualities further complicate the ongoing debate between amalgam and resin. Examples of resin include, glass ionomers, compomers, composite resin. The main difference in composition between these resins is the chemical attributes. Unlike amalgam fillings, the resin material contains desirable attributes such as fluoride release, wear resistance, low polymerization shrinkage, and low polymerization stress [Burgess 2011]. Fluoride strengthens the structure of the tooth, the low shrinkage sometimes occurs after filling is completed, where the material shrinks allowing bacteria to enter the cavity again, and the more a material is resistant to stress, the less likely the polymerization shrinkage will occur. Therefore, the use of amalgam and resin fillings can be determined based on the type of procedure involved.
Amalgam restorations
Posterior amalgam restorations have declined in popularity recently, but their usage must not be completely ignored. Amalgam fillings have a history of clinical success. To start with, an amalgam has good moisture tolerance since it does not bond to tooth structure chemically [Burgess 2011]. Therefore, the restoration procedure is much simpler, because it is not necessary to keep the tooth isolated and in dry conditions like in resin restorations. Since amalgam is a metal alloy it has the typical properties of metals, an amalgam filling is malleable and can be easily formed into shape of tooth, but at the same time it is also strong and durable. Limitations include galvanism [Burgess 2011], where a battery effect occurs in the mouth. It is caused by the amalgam’s composition of two metals, usually silver and mercury, in liquid medium, saliva. This scenario produces an electric current, which then leads to the break down of the amalgam filling. Other limitations caused by the amalgam’s metal properties are high thermal conductivity and the absence of adhesion to dental tissue [Burgess 2011], which often requires the additional removal of healthy tooth structure. The last main deterrent is its poor esthetics, and amalgam fillings are used typically on posterior restorations.In one of the first population-based studies conducted [Correa 2012], individuals with different types of restorative materials were interviewed and their responses were quantified. It was possible to divide individuals with composite fillings vs. those with resin restoratives based on factors such as their education level, socio-economic status, gender, cultural background, and age [Correa 2012]. Molar teeth are associated more frequently with amalgam fillings, which is a logical conclusion. However, since dentists rely on adhesives more often currently in combination with the resin compound, more people have been accepting it when they have an increased number of tooth surfaces in need of restoration.
The metal properties of alloy of an amalgam, allow it to simply be maneuvered to fit into the cavity for the restoration. There is no chemical bond; the amalgam and the cavity of the tooth fit together like two pieces of a puzzle. In resin fillings, on the other hand, bonding material must be applied before the resin in order to form a chemical bond between the tooth surface and the resin. Amalgam does not require a bonding material, but one has been developed called the bonded amalgam technique using adhesives. The most successful kind is called “4-META-based Amalgambond Plus (Parkell)”. It works by having a bonding agent bond to dentin with a hybrid layer. Dentin is the second layer of the tooth from outside in that comes after the outermost layer, enamel, which forms the crown visible on the outside [see Fig.1] [Burgess et al 2011]. The bonding resin to amalgam attachment is still mostly mechanical, not chemical. In 1992, as part of a study, the average bond strength between the existing amalgam and the new amalgam with Amalgambond (Parkell) was 105.68 kg/cm2 (10.37 MPa)[Chang 2004]. Therefore, the combination of both a mechanical bond of the amalgam filling, as well as the new Parkell bonding agent can allow the restored tooth to better resist fracture.
[fig. 1: [Human tooth. (2012, December 7). In Wikipedia, The Free Encyclopedia. Retrieved 08:45, December 7, 2012, fromhttp://en.wikipedia.org/w/index.php?title=Human_tooth&oldid=526877761]
Resin Restorations
The material selection for both posterior teeth restoration with resin compounds as well as that with amalgam is dependent upon the same factors: the patient’s age, caries (cavity) risk, esthetic requirements, how well the tooth can be isolated, and functional demands of the restoration [Burgess 2011]. In resin types, compomers, glass ionomers, and composite resins have the ability to bond to the tooth structure chemically, reinforce the tooth, fulfill esthetic requirements, behave as good thermal insulators and have fluoride release. On the other hand, a resin reconstruction procedure especially on molars has clinical limitations. It requires more time and attention to detail. Additionally, there are postoperative risks of polymerization shrinkage [Davidson, 1997] possible as a result of difficult procedure where there can be poor adhesive placement, all of which lead to possible leakages at the tooth surface and tooth sensitivity.There is a category of resin materials that has a stronger ability to release fluoride. This is a very important quality, because fluoride is a natural element included in toothpaste, as well as some water supplies that strengthens the tooth structure. Fluoride application is the most effective way of preventing caries and plaque, especially in the primary, developing teeth of children. Therefore, if the element is present in high amounts in a tooth filling as well, then the filling not only seals the cavity from destroying the tooth further, but it also strengthens the tooth in order to protect it against future caries.
A tooth’s structure made up of enamel, dentin, and pulp, constantly undergoes demineralization and remineralization processes. The 2mm thick outermost enamel layer consists of 96% calcium hydroxyapatite, 3% water and 1% proteins and lipids [Choi 2010]. During dental erosion, the enamel surface undergoes irreversible acidic dissolution. This is where the additional calcium fluoride layer [Gibson, 2011], made possible by the release of fluoride, would protect the regularly bare enamel surface. Bacteria are not involved in the erosion process. Instead, acids present in the food that we consume decalcify the enamel layer and leave the normally smooth tooth with an irregular surface. This effect is called “acid-etching” [Choi 2010].
The exact chemistry behind fluoride’s stellar protection of tooth enamel is still under debate. However, it is known that in already affected teeth, fluoride acts to reduce caries. It can do this by preventing bacteria from metabolizing carbohydrates on the enamel of the tooth [Gibson 2011]. Fluoride may also stimulate remineralization of the tooth, especially when exposed to increased levels of acid. This would in turn protect the tooth and reduce the tooth’s solubility after acid-etching.
It is possible, then, that fluoride can still offer protection to a healthy tooth. That is the theory behind how fluorination may still be useful to healthy permanent teeth in addition to healthy, developing primary teeth. The second step described above demonstrates the protective action of a fluoride-releasing resin material. Specifically, a material that allows the uptake of fluorine from the environment has a high “fluoride recharge,” or it may have the opposite, a high “fluoride release.” With added fluoride from the filling, for example, the tooth can then reduce caries in the other two ways. For the last step, the possible mechanism of action to reduce “the tooth’s solubility during subsequent acid attacks” , such as the erosive process, is the formation of a calcium fluoride layer forms in order.
The types of fluoride-releasing materials for restoration are glass ionomers, high-viscosity glass ionomers, resin-modified glass ionomers, and compomers. Glass ionomers release high levels of fluoride but they have low bond strengths, low wear resistance and medium fluoride recharge. In order to increase their bond strength, a conditioner or primer, usually a weak inorganic acid, is added to the tooth surface prior to the bonding process. This kind of conditioner is called an adhesive as well[Van Meerbeek 1998]. Using this kind of “super-glue” for teeth has become increasingly popular, and as a result, many clinical studies were conducted to test the effectiveness of different types [Tyas 2004]. High-viscosity glass ionomers release high levels of fluoride, have medium bond strength, overall strength, wear and fluoride recharge. The fluoride releasing composites, ironically, release low levels of fluoride and have a low fluoride recharge. They are not appropriate for a high caries risk patients, even though they also have the best wear resistance and toughness out of the fluoride releasing materials. The resin-modified glass ionomers have nanofillers added. This reduces particle size, and thus, creates a smoother, more esthetic appearance. Its release high levels of fluoride also increases long-term survival of the tooth and filling and is therefore, appropriate for a high caries risk patient. Compomers consist of a blend of resin composite and glass ionomers. They are successful to use on children’s teeth [Tran 2003] because the bonding system for compomers uses adhesive. This blocks some of the fluoride uptake in dentin, allowing for most of the fluoride from the compomer to be released on outer tooth surface. The primary and developing teeth of children need more protection on the outer surface as they begin to grow. Additionally, even though the mercury fumes from amalgam have proved to be harmless by many studies, parents still prefer that their children opt for the “safer” and more aesthetically pleasing resin tooth-colored materials [Tran 2003].
Composite resin is another choice of resin that has its own set of setbacks. It was not a very popular choice for posterior restorations because of its poor wear resistance. It was mainly used on bicuspids (premolars) because of its esthetic appeal. Over time, however, clinical trials testing wear resistance gained positive results and the popularity of the resin grew. con: composite resin shrinkage during polymerization [Bausch 1982]. Shrinkage causes eventual breakdown and thermal sensitivity. In order to decrease this effect, it is possible to use an elastic resin base layer of a lowly viscous substance before administering the composite resin, so that the strain will be minimized[Bausch 1982]. Another method used to decrease shrinkage is using LED lights. The procedure of the filling with composite resin involves placing visible light cured composite is placed in prepared cavity and curing it with light in 2mm increments. There are photoinitiators in the resin made of camphoroquinone, usually in the presence of an amine accelerator or catalyst. They are are activated by the visible light and the catalyst. This activated diketone causes the dimethacrylate resin monomers to polymerize. However, if there is a combination of photoinitiator types, there may be a problem because they need to absorb different wavelengths of light in order to react. Usually LED lights are used but quartz-tungsten-halogen or plasma arc curing lights polymerize all photoinitiators. Often the wrong type of light is used, which leads to low wear resistance in the final cured product.
Flowable composites are similar to composite resins, but with a lower viscosity. The flowable composites contain a lower filler load which allows them to better adhere to the cavity surface. There have been many studies conducted about whether this may reduce polymerization stress, but no clear consensus based on numerous has been reached. [Chung 2004]. A drawback of this material is that the lower filler load may reduce wear resistance. However, the percentage of filler may be chosen relative to type of tooth in concern. Flowable composites have higher polymerization shrinkage than composite resins because the flowables are more elastic [Davidson 1997]. It would make sense then, that they provide stress relief . However, since this has not yet been proven, the main use of this composite is for cavity adaptation. Unfortunately, in composite resins the polymerization shrinkage is about 3.7%-0.9%. There was a study conducted on six commercially available composite resins, each that were activated either either where the polymerization shrinkage was measured using a dilatometer and a mercury-filled capillary.
A new low stress material has been invented that reduces the internal stress from polymerization shrinkage. This substance can now be polymerized in 2mm instead of 4mm. The basis behind the SDR technology is the Polymerization modulator, which is embedded chemically in the resin backbone. This modulator interacts with the photoinitiator (usually camphorquinone) to regulate a slow modulus development, while at the same time still allowing a steady rate of polymerization or conversion of the material. Before SDR, the only way to control the modulus was by regulating the overall modulus development. This modulator allows more linear and branching chain propagations and conversions in the polymerization process.
Conclusion
Amalgam usage may have decreased, because the resin composite has grown, branched, and evolved to become a viable and aesthetic replacement; however, each restorative material has its own specific benefits and disadvantages. In the end, the type of material for reconstruction should be personalized to each clinical situation and needs of the patient. The increased number of studies and new developments in esthetic composite resins that cause low polymerization shrinkage, low stress, increased durability etc., present the patient with a variety of more appealing options, as opposed to simply black or white, amalgam or resin. Finally, as a result of the competition to concoct the ideal restorative, the accuracy in their chemical and physical properties of posterior restoratives has increased because of the strong competition for the ideal material.Works Cited
Bates, M. N. (2006). Mercury amalgam dental fillings: An epidemiologic assessment. International Journal of Hygiene and Environmental Health, 209(4), 309-316. [DOI ]
Bausch, J. R., de Lange, K., Davidson, C. L., Peters, A., & de Gee, A. J. (1982). Clinical significance of polymerization shrinkage of composite resins. The Journal of Prosthetic Dentistry, 48(1), 59-67. [DOI ]
Chang, J. C. (2004). Amalgam repair with a 4-META resin. The Journal of Prosthetic Dentistry, 92(5), 506-507. [DOI ]
Choi, S., Cheong, Y., Lee, G., & Park, H. (2010). Effect of fluoride pretreatment on primary and permanent tooth surfaces by acid-etching. Scanning, 32(6), 375-382. [DOI ]
Chung, S. M., Yap, A. U. J., Koh, W. K., Tsai, K. T., & Lim, C. T. (2004). Measurement of poisson's ratio of dental composite restorative materials. Biomaterials, 25(13), 2455-2460. [DOI ]
Correa, M. B., Peres, M. A., Peres, K. G., Horta, B. L., Barros, A. D., & Demarco, F. F. (2012). Amalgam or composite resin? factors influencing the choice of restorative material. Journal of Dentistry, 40(9), 703-10. [DOI ]
Davidson, C. L., & Feilzer, A. J. (1997). Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives. Journal of Dentistry, 25(6), 435-440. [DOI ]
Lubisich B. Erinne, Thomas J. Hilton, Jack L. Ferracane, Hristina I. Pashova, & Bruce Burton. (2011). Association between caries location and restorative material treatment provided. Journal of Dentistry, 39(4), 302-308. [DOI ]
Gibson, G., Jurasic, M. M., Wehler, C. J., & Jones, J. A. (2011). Supplemental fluoride use for moderate and high caries risk adults: A systematic review. Journal of Public Health Dentistry, 71(3), 171-184. [DOI ]
Giovannetti, A., Goracci, C., Vichi, A., Chieffi, N., Polimeni, A., & Ferrari, M. (2012). Post retentive ability of a new resin composite with low stress behaviour. Journal of Dentistry, 40(4), 322-328. [DOI ]
Ilie, N., & Hickel, R. (2011). Investigations on a methacrylate-based flowable composite based on the SDR™ technology. Dental Materials, 27(4), 348-355. [DOI ]
John O Burgess, & Deniz Cakir. (2011). Material selection for direct posterior restoratives. Dental Economics, 101(9), 34A-34A,35A,36A,37A,38A,39A,40A,41A,42A,43A,44A,45A. [pdf ]
Lambrechts, P., Goovaerts, K., Bharadwaj, D., De Munck, J., Bergmans, L., Peumans, M., & Van Meerbeek, B. (2006). Degradation of tooth structure and restorative materials: A review. Wear, 261(9), 980-986. [DOI ]
SABATINI, C., CAMPILLO, M., & AREF, J. (2012). Color stability of ten resin-based restorative materials. Journal of Esthetic and Restorative Dentistry, 24(3), 185-199. [DOI ]
Tran, L., & Messer, L. B. (2003). Clinicians choices of restorative materials for children. Australian Dental Journal, 48(4), 221-232. [DO I]
Tyas, M., & Burrow, M. (2004). Adhesive restorative materials: A review. Australian Dental Journal, 49(3), 112-121. [DOI ]
Van Meerbeek, B., Perdigão, J., Lambrechts, P., & Vanherle, G. (1998). The clinical performance of adhesives. Journal of Dentistry, 26(1), 1-20. [DOI ]
Wang, W., DiBenedetto, A. T., & Jon.Goldberg, A. (1998). Abrasive wear testing of dental restorative materials. Wear, 219//(2), 213-219. [DOI ]